Wei Zhang

Chiral metasurfaces with tailorable chiroptical responses are of great interest for applications in many fields. However, most previous studies on non-Hermitian chiral metasurfaces have focused on the realization of exceptional points, where the strong circular dichroism (CD) is often accompanied by low transmission. Here, we propose a gain-assisted non-Hermitian approach to achieve near-perfect optical chirality in a Born–Kuhn-type plasmonic metasurface. The structure consists of bilayer, orthogonally oriented silver nanorods integrated with an optical gain medium. Guided by a coupled-oscillator model, we show that the interplay between geometrical chirality and gain-induced non-Hermitian coupling enables precise control of the interlayer interaction and modal hybridization. As a result, a CD value as high as 0.999 is obtained at 1550 nm, while a high transmission of 0.988 for the selected circular polarization is maintained. Furthermore, leveraging the plasmon-enhanced local fields, a pronounced handedness-selective third-harmonic generation response is theoretically demonstrated. This work provides a strategy for high-efficiency chiral photonic devices and opens opportunities for potential applications in chiral molecular detection, ultrasensitive sensing, chiral logic, superchiral fields, and chiral nonlinear optics.

Strong light-matter interaction in plexcitonic systems plays a crucial role in both fundamental quantum optics study and practical applications, including quantum information processing and nanophotonic devices. However, despite strong light confinement associated with plasmons, large damping of plasmonic cavities remains a major obstacle to achieving strong coupling, particularly with single exciton. Here, we introduce a novel platform that achieves strong coupling via leveraging dark plasmon mode to reduce the loss of the system rather than only enhancing the coupling strength to overcome the system’s large damping. Optical properties of the bright/dark modes supported by different silver nanorod dimers are studied, revealing the connection between symmetric configurations and the properties of these resonant modes. The dark mode of side-by-side silver nanorod dimer exhibits an ultralow loss of approximately 22 meV, dramatically decreasing the harsh requirement in coupling strength and enabling strong coupling with a single quantum dot. The time-domain and frequency-domain characteristics of the bright/dark mode-exciton coupling system are compared in detail. Furthermore, a new scheme based on symmetry breaking is proposed to realize the coupling state control across three coupling regimes with different time-domain and frequency-domain characteristics.

Organic light-emitting diodes (OLEDs) supporting the direct emission of circularly polarized (CP) light are essential for numerous technologies. The realization of CP-OLEDs with large dissymmetry (g _EL) factors and high external quantum efficiencies (EQEs) has been accepted as a considerable challenge. Here we demonstrate the realization of efficient CP-OLEDs based on the assembly of chiral plasmonic nanoparticles (NPs) and supramolecular aggregates. The chiral plasmonic NPs serve as the chiral scaffold and chiral optical nanoantenna to modulate the circularly polarized absorption and emission of the supramolecular chromophores. We employ different chiral plasmonic NPs to construct various CP-OLEDs with the emission dominated by chiral excitons or chiral plasmons. The CP-OLED showing a high EQE of 2.5% and a large g _EL factor of 0.31 is achieved, as a result of multiscale chirality transfer, plasmonic enhancement, and the suppression of the overshoot effect. The proposed schemes are compatible with the current manufacturing technology of OLEDs. This work demonstrates that chiral plasmonic NPs can be promising candidates in chiral photoelectric devices.

Flat optics of uniform phase gradient metasurfaces based on the generalized Snell’s law has been extensively studied. The optics of nonuniform phase gradient metasurfaces (NPGMs) is less clear. Here based on Huygens’ principle and finite-difference time-domain (FDTD) simulation, we explore the optical properties of NPGMs made of nanorods (meta-atoms), which can be tuned by modulation of propagation phase and geometric phase. It is found that the nonuniformity of phase gradient may lead to multichannel anomalous reflection/refraction. The multiple beam splitters with arbitrary intensity ratio can be achieved by using the amplitude/phase modulation. Based on our design principle, we can obtain different anomalous reflection patterns (with channels ±1, ±2, both ±1 and ±2, or no reflection at anomalous angle) by different arrangement of just two types of meta-atoms. In addition, we are able to achieve chiral anomalous reflections for designed NPGMs made of nanorods and L-shaped nanoparticles. Our formulism provides general design guidance for NPGMs and can be used to realize the beam splitting function with adjustable angle and intensity ratio.